rotation in CHOPS

[pasto]

Hello,

 

Struggling hard to import rotation channels in CHOPS in H15. Sounds simple but pretty nothing works for me.

I must be missing something obvious. Are R then rx ry rz valid channels to import in a geometry node related to a simple transform SOP ?

Even a simple right clic then lag in the menu doesn't make anything but stops any rotation.

Quite lost

 

Many thanx.

[jrockstad]

The Geometry CHOP is actually only concerned with the attributes on the geometry itself and does not take into account parameters on the specific node it may be reading from, so setting 'R' in the attribute field would not be valid as it is not a standard attribute in Houdini. The Rename Scope parameter really is just creating channels from the specified attribute, and you actually could name them anything you want, something like tx, ty, tz for example is simply conventional. To get those channels back into SOP level you then need a Channel SOP which updates geometry attributes by associating them with the channels created by the Geometry CHOP. 

 

Basically, the Geometry CHOP / Channel SOP workflow is for operating on points, for directly modifying SOP parameters you would use the Export CHOP tied to a Transform SOP, for example. I've attached a small scene demonstrating this.

 

Hope that helps - CHOPs can definitely be confusing at first but it's a very unique and powerful aspect of Houdini so I hope you stick with it. 

chops_demo.hiplc

[malexander]

The Object CHOP is very helpful for getting the combined rotation of an object and its parents, if that's what you're looking for.

[pasto]

Thanx a lot John and Mark,

 

I wanted to get rotation values in CHOPS, let's say you have animated the normals (vector), or an orient attribute (quaternion) of points in order to get some copies to inheritate those rotations. I entered the orient attribute in a geometry CHOP, set it to float 4 and then added some noise to it. In a matter of facts it works perfectly I didn't know why it didn't in my first try, sorry.

 

But now I have another problem, of course my noise is disturbing the 4 values coming from the orient attribute, how can I affect only the first one ? I tried a delete CHOP with something like ty* tz* tw* (which are my 3 channel names) but it kills the effect, and my copy is not working anymore.

 

Many thanx

 

(And yes indeed CHOPS seem to be amazingly useful)

 

CHOP_ROT.hiplc

[jrockstad]

In your Channel SOP, set Channel Scope to tx and Attribute Scope to orient(0), this specifies to only grab the tx channel and use it to modify the value at the first index of the orient attribute. 

[malexander]

But now I have another problem, of course my noise is disturbing the 4 values coming from the orient attribute, how can I affect only the first one ? I tried a delete CHOP with something like ty* tz* tw* (which are my 3 channel names) but it kills the effect, and my copy is not working anymore.

 

Most CHOPs have a Scope parameter in the Common tab, set to "*". Change it to the channel names you want to affect, wildcards are also accepted there.

[pasto]

A big thank you.

 

My Houdini animation knowledge needs a serious improvement I guess, any thought about a nice learning ressource aimed towards this specific part, Animation editor, Chops and even channels in general ? We find too much stuff about fancy explosions and very few about the core animation system which looks pretty deep.

 

Anyway thanx a lot.

[edward]

For CHOPs, there's Andrew Lowell's book http://www.andrew-lowell-productions.com/andrew-lowell-productions/resources.html

[pasto]

Yes, thanx, looks great indeed.